/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package it.ap.sa.core.configuration.commons;

import java.util.Iterator;
import java.util.NoSuchElementException;

/**
 * * A specialized iterator implementation used by {@link AbstractConfiguration}
 * to return an iteration over all keys starting with a specified prefix.
 *
 * <p>
 * This class is basically a stripped-down version of the {@code FilterIterator}
 * class of Commons Collections
 * </p>
 *
 * @author <a href="http://commons.apache.org/configuration/team-list.html">
 *         Commons Configuration team</a>
 * @version $Id: PrefixedKeysIterator.java 1205603 2011-11-23 21:17:38Z oheger $
 */
class PrefixedKeysIterator implements Iterator<String> {
	/** Stores the wrapped iterator. */
	private final Iterator<String> iterator;

	/** Stores the prefix. */
	private final String prefix;

	/** Stores the next element in the iteration. */
	private String nextElement;

	/** A flag whether the next element has been calculated. */
	private boolean nextElementSet;

	/**
	 * Creates a new instance of {@code PrefixedKeysIterator} and sets the
	 * wrapped iterator and the prefix for the accepted keys.
	 *
	 * @param wrappedIterator
	 *            the wrapped iterator
	 * @param keyPrefix
	 *            the prefix of the allowed keys
	 */
	public PrefixedKeysIterator(Iterator<String> wrappedIterator, String keyPrefix) {
		iterator = wrappedIterator;
		prefix = keyPrefix;
	}

	/**
	 * Returns a flag whether there are more elements in the iteration.
	 *
	 * @return a flag if there is a next element
	 */
	public boolean hasNext() {
		return nextElementSet || setNextElement();
	}

	/**
	 * Returns the next element in the iteration. This is the next key that
	 * matches the specified prefix.
	 *
	 * @return the next element in the iteration
	 * @throws NoSuchElementException
	 *             if there is no next element
	 */
	public String next() {
		if (!nextElementSet && !setNextElement()) {
			throw new NoSuchElementException();
		}
		nextElementSet = false;
		return nextElement;
	}

	/**
	 * Removes from the underlying collection of the base iterator the last
	 * element returned by this iterator. This method can only be called if
	 * {@code next()} was called, but not after {@code hasNext()}, because the
	 * {@code hasNext()} call changes the base iterator.
	 *
	 * @throws IllegalStateException
	 *             if {@code hasNext()} has already been called.
	 */
	public void remove() {
		if (nextElementSet) {
			throw new IllegalStateException("remove() cannot be called");
		}
		iterator.remove();
	}

	/**
	 * Determines the next element in the iteration. The return value indicates
	 * whether such an element can be found.
	 *
	 * @return a flag whether a next element exists
	 */
	private boolean setNextElement() {
		while (iterator.hasNext()) {
			String key = iterator.next();
			if (key.startsWith(prefix + ".") || key.equals(prefix)) {
				nextElement = key;
				nextElementSet = true;
				return true;
			}
		}
		return false;
	}
}
